Digitaria thailandica B. Boonsuk, Chantar. & Hodk., 2014

Boonsuk, Boonchuang, Chantaranothai, Pranom & Hodkinson, Trevor R., 2014, A new species and two new taxon records of Digitaria (Poaceae: Panicoideae) for Thailand, Phytotaxa 161 (4), pp. 283-288 : 283-287

Digitaria thailandica B. Boonsuk, Chantar. & Hodk. , sp. nov. ( Fig. 1 )

D. thailandica is similar to D. junghuhniana and D. thyrsoidea in having many racemes with a long common axis and brown upper florets but differs in its perennial habit, long setae on racemes, triangular lower glume, lanceolate, truncate and 3- nerved upper glume and inequidistant nerves on lower lemma ( Fig. 2 , A–C; Table 1).

Type:— THAILAND. Loei: Phu Ruea, San Tom , elevation ca. 750 m, 3 November 2011, B. Boonsuk 590 (holotype KKU!; isotypes BK!, BKF!, K!) .

Perennial grass. Culms tufted, rhizomatous, ascending to erect, 75–120 cm high, rooting at lower nodes; nodes and internodes glabrous. Sheaths glabrous to pilose on the upper part, 4–12 cm long, usually longer than internodes. Ligules membranous, 2–6 mm high, entire to erose. Blades linear, 6–20 cm × 5–15 mm, chartaceous, base rounded with bulbous based setaceous hairs, apex acuminate, margin sinuate, chartaceous; abaxial surface scabrous, pale green, adaxial surface scabrous. Racemes 7–13, subdigitate, sometimes whorled at the lower racemes, the longest raceme 9–21 cm long; rachis triquetrous, 0.3–0.5 mm wide, serrate, setose especially toward the base of racemes; common axis 2.5–6 cm long. Pedicels triquetrous, spicular, abscission cupuliform. Spikelets binate, homomorphous, elliptic-lanceolate, 3–3.2 × 0.8–0.9 mm; pubescent, hairs smooth. Lower glume a triangular scale, 0.25–0.3 mm long; apex acute. Upper glume oblong, 0.5–1 mm long, apex truncate, chartaceous; pubescent along the nerves, nerves 3, equidistant. Lower floret sterile; lemma as long as the spikelet, apex acute, chartaceous, nerves 7, inequidistant; pubescent along the nerves but with broadly glabrous interspaces on either side of midnerve; palea membranous, 0.6–0.8 mm long. Upper floret hermaphrodite, brown when mature; lemma slightly convex, 2.8–3 mm long, apex acuminate, coriaceous to cartilagenous; palea similar to lemma but slightly shorter. Lodicules truncate, ca. 0.3 mm long. Anthers 1–1.4 mm long, yellowish to brownish. Caryopsis ellipsoid, 1.5–1.8 × 0.5–0.6 mm, yellowish to brownish.

Distribution and habitat: — Digitaria thailandica is endemic to northern and north-eastern Thailand. It grows in shady areas of dry evergreen and bamboo forests, at elevations between 300 and 1,000 m.

Phenology: —Flowering in June–November.

Etymology: —The specific epithet reflects the known occurrence of the species in Thailand.

Vernacular: —Thai: Ya tin nok.

Note: — Digitaria thailandica is closely related to D. junghuhniana and D. thyrsoidea . They share a lax and open inflorescence, many racemes which are distant along an elongate common axis or whorled at the base and the upper florets are brown to dark brown (when mature). It differs from these species in a number of characteristics, notably those of its perennial habit, setae on racemes, lower and upper glumes and lower lemma ( Table 1).

Additional specimens examined:— Thailand. Uthai Thani: Huai Kha Khaeng Wildlife Sanctuary , 18 July 1991, K. Chayamarit 550 ( BKF) ; Phetchabun: Nam Nao National Park , 22 January 2011, B. Boonsuk 558 ( BK. BKF, KKU) ; Loei: Na Haeo National Park , 20 June 1965, W. Nanakorn et al. 3826 ( QBG) ; Phu Ruea National Park , 11 October 2009, B. Boonsuk 147 ( BK, BKF, KKU, QBG) ; Phitsanulok: Phu Hin Rong Kla National Park , 11 September 2010, B. Boonsuk, P. Phonsena & P. Kochaiphat 409 ( BK, BKF, KKU, QBG) .

Digitaria setigera Roth ex Roemer & Schultes (1817: 474) var. calliblepharata (Henrard) Veldkamp (1973: 40) .

Digitaria microbachne (J. Presl) Henrard (1830: 13) subsp. calliblepharata Henrard (1950: 452) . Type:— INDONESIA, Kangean Arch., C.A. Backer 27997 (holotype: L!; isotype BO!).

Digitaria timorensis (Kunth) Balansa (1890: 138) subsp. blepharophora Henrard (1950: 747) . Type:—TIMOR, C. Gaudichaud s.n. (holotype P!).

Distribution and habitat: — Digitaria setigera var. calliblepharata is rare. It is distributed in India, Thailand, Malaysia, Singapore, Indonesia, the Philippines and Guam, on sandy soils in open areas, and elevations between 200 and 600 m in Thailand.

Phenology:— Flowering September–February.

Vernacular: —Thai: Ya tin nok khon thong.

Note: — Digitaria setigera var. calliblepharata is here reported to occur in Thailand for the first time. Two Thai collections were found only in Loei province. The spikelets of this variety are homomorphous and pubescent with setaceous hairs on the lower lemma. The setaceous hairs are usually bulbous based ( Fig. 2 , D–F). Its lower glume is usually absent but sometimes occurs as a triangular minute scale.

Additional specimens examined. — THAILAND. Loei: Nong Hin , 13 September 2009, B. Boonsuk 137 ( BKF, K, KKU) ; Phu Kradueng National Park , 8 November 2010, B. Boonsuk 463 ( BK, BKF, KKU) . INDONESIA. Java: Kota Bogor , 28 October 1949, J.H. Kern 7275 ( BO) ; 8 November 1952, W. Meijer 1288 ( BO) ; Java Timur , 13 January 1918, C.A. Backer 24416 ( BO) ; Pasoeroean , 11 July 1918, J.G.B. Beumée 2818 ( BO) ; Kangean Arch. , 2 May 1919, C.A. Backer 29404 ( BO) ; Bali, 21 August 1972, J.F. Veldkamp 6038 ( BO) ; West Timor: Soe, 19 July 1949, Ch. Monod de Froideville 1007 ( BO) ; Loli, 23 July 1949, Ch. Monod de Froideville 1013 ( BO) & 1088 (BO).

Digitaria thyrsoidea Balansa (1890: 138) . Type:— VIETNAM, Cam Ranh Bay , B. Balansa s.n. (holotype L!;

isotype P!).

Digitaria quinhonensis A. Camus (1921: 456) . Type:— VIETNAM, Annam , Quinhon ,

B. Balansa s.n. (holoype L!; isotype P!).

Paspalum subcorymbosum A. Camus (1912: 223) . Digitaria subcorymbosa (A. Camus) A. Camus (1922: 406) . Type:— CAMBODIA, Pursat, M. Godefroy 382 (holotype P!, photo in K!).

Distribution and habitat: — Digitaria thyrsoidea is distributed in Thailand, Laos, Cambodia and Vietnam in evergreen and deciduous forests, at elevations between 300 and 600 m in Thailand.

Phenology:— Flowering in May–November.

Vernacular: —Thai: Ya tin nok cho kang.

Note: — Digitaria thyrsoidea is characterized by having slender pedicels, membranous, truncate and 1-nerved upper glume and equidistant nerves with short hairs along the nerves on the lower lemma ( Fig. 2 , G–I). Digitaria quinhonensis , D. subcorymbosa and D. thyrsoidea were classified by only the characters of upper glume ( Henrard 1950) but they have similar inflorescences and spikelets, especially lower lemma characteristics. Veldkamp (1973) also suggested that they are forms of the single species, D. thyrsoidea . This is in agreement with Lazarides (1980) who treated D. quinhonensis and D. subcorymbosa as synonyms of D. thyrsoidea . The Thai specimens, reported here, extend the range of D. thyrsoidea from Indo-China ( Camus & Camus 1922) west to northeastern Thailand. This is the first time the species has been recorded in Thailand.

Specimens examined: — THAILAND. Phetchabun: Nam Nao National Park , 21 June 2008, B. Boonsuk 15 ( KKU) ; ibid., 15 May 2012, B. Boonsuk 631 ( KKU) ; Sakon Nakhon: Phu Phan National Park , 11 June 2009, B. Boonsuk 69 ( BKF, KKU) ; ibid., 26 September 2010, B. Boonsuk 427 ( BKF, KKU) ; Ubon Ratchathani: Phu Chong Na Yoi National Park , 9 July 2009, B. Boonsuk 99 ( BKF, KKU) .

Figures

FIGURE 1. Digitaria thailandica B. Boonsuk, Chantar. & Hodk., sp. nov. A. habit of flowering plant; B. sheath, blade and ligule; C. part of inflorescence, showing setae on rachis and the bases of racemes; D. rachis and pedicels; E. spikelet, abaxial face view; F. spikelet, adaxial view; G. upper floret, adaxial view; H. upper floret, abaxial view (from B. Boonsuk 590). Drawn by W. Thammarong.

FIGURE 2. SEM micrographs of Digitaria thailandica, D. setigera var. calliblepharata, and D. thyrsoidea. A–C. Digitaria thailandica: A. pedicels and rachis; B. spikelet abaxial face; C. spikelet adaxial face (from B. Boonsuk 590). D–F. Digitaria setigera var. calliblepharata: D. spikelet abaxial face; E. spikelet adaxial face; F. bulbous-based setaceous hairs on lower lemma (from B. Boonsuk 463). G–I. Digitaria thyrsoidea: G. pedicels and rachis; H. spikelet abaxial face; I. spikelet adaxial face (from B. Boonsuk 427). Scale bar: A–E & G–I = 200 µm, F = 30 µm.